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Oct. 12, 2011 -- Two more deaths have been reported in the ongoing outbreak of listeria food poisoning from Colorado cantaloupes.

As of Oct. 11, the CDC received reports of 23 deaths among 116 people infected with one of the four outbreak-related strains of Listeria monocytogenes. The bacteria can cause a deadly disease known as listeriosis.

It's now the second largest listeria outbreak in U.S. history. The largest U.S. listeria outbreak was in 1985, when 142 people became ill after eating Mexican-style cheese contaminated with unpasteurized milk.

Four of the illnesses in the current outbreak involved a pregnancy. Three pregnant women became ill during the outbreak, and listeria infection was diagnosed in one newborn. One of the pregnant women had a miscarriage because of the infection.

Pregnant women are at high risk of listeriosis. Also at risk are people over age 60, people with diabetes or diseases that weaken the immune system, and people taking drugs that suppress the immune system.

The current outbreak of listeria from cantaloupes isn't over, even though it's very unlikely that any of the contaminated cantaloupes are still in refrigerators or on grocery shelves. Melons from Jensen Farms' Granada, Colo., packing plant were last shipped on Sept. 10. Cantaloupes have only about a two-week shelf life.

Listeriosis Symptoms

Although listeriosis is a food-borne illness, when symptoms appear it usually means the bacteria have escaped the digestive tract and are spreading throughout the body. Listeriosis sometimes results in fatal meningitis or encephalitis.

Listeriosis usually begins with diarrhea or other intestinal symptoms. Patients soon develop fever and muscle aches. What happens next depends on a person's risk factors:

While pregnant women usually get a mild flu-like illness, listeria infection can cause miscarriage, stillbirth, premature delivery, or fatal infection of the newborn.

Symptoms may occur as soon as soon as three days or as long as two months after infection. The usual incubation period is thought to be one to three weeks.

Foods typically linked to listeriosis are deli meats, hot dogs, and soft cheeses made with unpasteurized milk. Produce is less often linked to outbreaks, although listeria occurs in soil and water. Listeria bacteria are killed by cooking, but they can grow and multiply in refrigerators.

In refrigerators where listeria-contaminated foods have been stored, other foods often become contaminated. So does the refrigerator itself, which should be thoroughly cleaned with soap and water and then wiped down with a solution of diluted bleach.